AWESOME receiver system narrowband VLF data

Most of the data is collected on two air-core loop antennas, oriented orthogonal, to collect the two horizontal components of the magnetic field. The north-south, or N/S antenna is sensitive mostly to waves arriving from the north of from the south direction, meaning it picks up the magnetic field component in the east-west direction. The other antenna is the east-west antenna, which is the opposite. Narrowband data are the amplitudes and phase of specific frequencies, usually corresponding to VLF transmitters that are used for communications and navigation. Sampling rate is usually either 1 Hz or 50 Hz. They are also useful as a diagnostic of the ionosphere. Most of these transmitters use minimum shift keying (MSK) modulation, and the recording software extracts the amplitude, and the phase is calculated by demodulating the MSK demodulation. Details of the demodulation algorithm and examples of its application can be found in Gross, N.C.; Cohen, M.B.; Said, R.K.; Golkowski, M, "Polarization of Narrowband VLF Transmitter Signals as Ionospheric Diagnostic", JGR, 2018, 901-917. https://doi.org/10.1002/2017JA024907